The present invention relates to a printing system for formation of images on both planes or surfaces of a web.
Print systems for forming images on both faces of webs, typically including elongate continuous strip-shaped paper sheets, are known. One of these systems is disclosed, for example, in Japanese Application Patent Laid-Open Publication No. Hei 8-50429, wherein a couple of separate printer devices are serially disposed for performing printing operations in such a way that printing is first performed on a first plane (top surface) of a web at one printer device forming a front stage; and then, after the web discharged from the front-stage printer device is turned over by an inversion device so that its top surface becomes a bottom or back surface, the web is supplied to the second printer device at a post stage, at which printing is carried out on a second plane (back surface) of the same web.
Prior known webs that are adaptable for use with printing systems of the type described above may generally include a so-called xe2x80x9ccontinuousxe2x80x9d paper sheet with feed holes along the opposite side edges thereof. Unfortunately, in cases where printing is carried out on such a continuous paper sheet with feed holes, there is a need after completion of the print operation to perform a paper-cutaway processing for cutting the feedhole-provided opposite edge portions away from the xe2x80x9cbodyxe2x80x9d of the printed paper sheet, which requires an increased length of time. The presently available approach to eliminating the timing-consuming and troublesome paper margin cutaway processing is to employ xe2x80x9cspecialxe2x80x9d printing systems that are capable of handling xe2x80x9cfeedhole-lessxe2x80x9d webs, i.e. webs without such feed holes, some of which systems are now becoming popular in the market.
Incidentally, in the printing systems described above, in case those systems are designed so that at least a printing device disposed at the front stage employs a printer apparatus of the type forming images by use of electrophotography, an additional heat-up process is inevitably required for fusion and photographic fixing of images (toner images) that have been transferred onto the web. Due to thermal action of this thermal fixation process, any web being fed into a printer apparatus of the post stage can experience unwanted thermal shrinkage so that its resultant size is less than that as measured in the original state thereof.
Upon occurrence of such thermal web-size reduction or shrinkage, the length of a page measured during top-surface printing becomes different from that during back-surface printing, resulting in production of awkward printed matter in which the top surface-side on-web image positions fail to be identical to those on the back surface thereof.
It should be noted that the web""s thermal shrinkage amount is different depending upon a variety of parameters including, but not limited to, the thickness values and sizes of webs used or, alternatively, the attachment amount of toner particles for creation of on-web images; thus, any techniques for conveying webs for forward transportation with prediction of possible thermal shrinkage amounts are no longer employable.
It is a primary object of the present invention to provide a new and improved printing system that is capable of accurately printing images in such a way that an image on a first plane or surface is identical to that on a second plane or surface even in cases where a web being extruded from a first printer apparatus is shrunk or expanded due to environmental conditions.
The foregoing object is attainable by providing a specific printing system which has a first printer apparatus for forming an image on a first plane of a web having no feed holes and a second printer apparatus provided at a post stage of the first printer apparatus for forming an image on a second plane of said web, wherein at least the first printer apparatus has mark formation means for forming a position alignment mark at a predesignated position on each page of said web, and wherein at least the second printer apparatus has mark detection means for detecting said position alignment mark and control means for generating a web feed control signal once per preset period and for causing the generation timing of said web feed control signal to be identical in phase with the generation timing of a mark detection signal issued from said mark detection means through detection of said position alignment mark.